.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright 2015-2016 Research Organization for Information Science
.\"                     and Technology (RIST). All rights reserved.
.\" $COPYRIGHT$
.TH MPI_File_set_atomicity 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_File_set_atomicity\fP \- Sets consistency semantics for data-access operations (collective).

.SH SYNTAX
.ft R
.nf
.SH C Syntax
.nf
#include <mpi.h>
int MPI_File_set_atomicity(MPI_File \fIfh\fP, int \fIflag\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
fh
File handle (handle).
.TP 1i
flag
\fBtrue\fP to enable atomic mode, \fBfalse\fP to enable nonatomic mode (boolean).

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
The consistency semantics for data-access operations using the set of
file handles created by one collective MPI_File_open is set by collectively
calling MPI_File_set_atomicity. All processes in the group must pass identical values for
.I fh
and
.I flag.
If
.I flag
is
.I true,
atomic mode is set; if
.I flag
is
.I false,
nonatomic mode is set.
.sp
The default value on a call to MPI_File_open in Open MPI is \fItrue\fP for jobs running on more than one node, \fIfalse\fP for jobs running on a single SMP. For more information, see the MPI-2 standard.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.

